Relevant art of the present invention is disclosed in the following literatures.
(1) A. S. Zolotko, V. F. Kitaeva, N. Kroo, N. N. Sobolev, L. Csillag, JETP.Lett., 32, 158 (1980).
(2) B. Y. Zel'dovich, N. V. Tabiryan, Sov. J. Quantum Electron., 10, 440 (1980).
(3) T. Ikeda, T. Sasaki, K. Ichimura, Nature, 361, 428 (1993).
(4) L. Komitov, K. Ichimura, A. Strigazzi, Liq. Cryst., 27, 51 (2000).
(5) L. Komitov, C. Ruslim, Y. Matsuzawa, K. Ichimura, Liq. Cryst., 27, 1011 (2000).
(6) L. Komitov, K. Ichimura, Mol. Cryst. Liq. Cryst., in press
(7) L. Komitov, O. Tsusumi, C. Ruslim, T. Ikeda, K. Ichimura, K. Yoshino, submitted to J. Appl. Phys.
(8) E. Santamato, Y. R. Shen, “Liquid Crystals for Nonlinear Optical Studies” in the book “Handbook of Liquid Crystal Research” Oxford University Press, New York, 1997.
(9) C. Ruslim, L. Komitov, Y. Matsuzawa, K. Ichimura, Jap. J. Appl. Phys., 39, L104 (2000).
(10) L. Komitov, J. Yamamoto, H. Yokoyama, J. Appl. Phys., 89, 7730 (2001).
(11) P. Jägemalm, G. Barbero, L. Komitov, A. K. Zvezdin, Phys. Rev. E, 58, 5982 (1998).
(12) P. Jägemalm, G. Barbero, L. Komitov, A. Strigazzi, Phys. Lett. A235, 621 (1997).
(13) M. Monkade, M. Boix, G. Durand, Europhys. Lett., 5, 697 (1988).
(14) B. Jerome, M. Boix, P. Pieranski, Europhys. Lett., 5, 693 (1988).
(15) P. Jägemalm, L. Komitov, Liq. Cryst., 23, 1 (1997).
(16) M. Nobili, PhD Thesis, 1992.
(17) M. Nobili, G. Durand, Europhys, Lett., 25, 527 (1994).
(18) P. Jägemalm, D. S. Hermann, L. Komitov, F. Simoni, Liq. Cryst, 24, 335 (1998).
(19) D. S. Hermann, P. Rudquist, K. Ichimura, K. Kudo, L. Komitov, S. T. Lagerwall, Phys. Rev. E, 55, 2857 (1997).                (20) Y. Matsuzawa, C. Ruslim. L. Komitov, K. Ichimura, Mol. Cryst. Liq. Cryst. in press.        
Liquid crystal is a very highly anisotropic material and has optical properties which can be very easily changed in accordance with various external factors such as electric and magnetic fields, mechanical flow, temperature, and light. In addition to the electro-optic effects, optically induced reorientation of the alignment of liquid crystal has drawn strong interest due to its potential for different device implementations in photonics. In general, there are two possible methods for affecting the alignment of liquid crystal by light so as to change light transmittance thereof. One of such methods is a way to use direct interaction between light and liquid crystal molecules, as is the photoexcited Fredericks transition, and the other method is an indirect photoexcitation method in which surface or bulk liquid crystal properties are changed by light.
The photoexcited Fredericks transition is caused by giant optical nonlinearity of liquid crystal and has drawn strong interest for these 20 years. In this case, when light imposes a direct and rotational torque on liquid crystal molecules, reorientation of the alignment thereof occurs in a predetermined direction. The direction in which the liquid crystal is aligned depends on various experimental conditions such as an alignment direction of liquid crystal before illumination, the thickness of a cell, and light intensity.
In recent years, photoinduced reorientation of the alignment of azobenzene liquid crystal was reported which is caused by the change in bulk or surface properties thereof resulting from photoexcitation.
A subject which is most closely related to the study carried out by the inventors of the present invention is a photoinduced anchoring transition of dichroic azobenzene liquid crystal that occurs resulting from the modulation of macroscopic surface anchoring conditions induced by the change in molecular shape during a photoisomerization process. That is, when the concentration of the azobenzene molecules adheres to the solid surface exceeds a certain level, the macroscopic alignment of liquid crystal is changed from the planar alignment to the homeotropic alignment. That is, as reported by the inventors of the present invention, after being transformed from trans-isomers to cis-isomers by photoisomerization, the azobenzene molecules are more likely to adhere selectively to a solid surface, and as a result, the anchoring conditions for the liquid crystal are changed. The reason for this is understood that since the molecular shape and the direction of molecular electron dipole moment of the trans-isomer are significantly different from those of the cis-isomer, a large polarity resulting from a bent molecular shape of the cis-isomer enhances the adsorption properties of the azobenzene molecules to the solid surface.
However, the modulation (photoregulation of the anchoring) of the surface anchoring conditions caused by photoexcitation is a continuous process, and hence it is not appropriate that this phenomenon itself is used as the principle of a light switching device. In fact, even before the transformation from the planar alignment to the homeotropic alignment caused by photoexcitation is observed, the continuous change in anchoring intensity, which depends on the light exposure time, can be clearly grasped by the change in voltage when the threshold voltage of the electric field induced Fredericks transformation is measured.